Patent GB-638091-A (GB)
Title: A process for the production of diketones
IPC: C07C49/784
Filed: 1947-08-05
Abstract: Ketimines in which the carbon atom linked by a double bond to the nitrogen atom is linked by single bonds to two other carbon atoms are treated with acylating agents, and the resulting acylated ketimine hydrolysed to form a diketone.  The ketimines used as starting materials may be obtained by condensing ketones with primary amines, catalytically reducing ketones in the presence of ammonia and hydrogen or dehydrogenating secondary amines.  The imines need not be isolated from the reaction mixture.  The groups attached to the carbon atom which is linked to the imino nitrogen atom may be alkyl, aryl or cycloalkyl, a number of each being specified; there must however be an active hydrogen atom which can react with the acylating agent. Alternatively, the ketimine may be derived from cyclopentanone or cyclohexanone or an alkyl-substituted derivative.  The free bond of the imino nitrogen atom may be joined to hydrogen or to an alkyl, aryl or cycloalkyl radical, a number being specified.  The acyl group normally attaches itself to the carbon atom in the a -position to the imino group, so that the product is a mono-imine of a b -diketone. If there is more than one acylatable carbon atom, a mixture of isomers may be formed, or, if the acylating agent is used in excess, di- and poly-acyl derivatives may be produced.  If the active hydrogen atom is easily replaceable, a carboxylic acid or ester may be used as acylating agent, in the latter case a condensing agent such as sodium ethoxide being preferably added.  In other cases a more powerful acylating agent is necessary such as an acid anhydride, acid halide or ketene, a number of suitable agents being mentioned; acetic anhydride, acetyl halides and especially ketene are preferred. A catalyst such as aluminium chloride or boron trifluoride may be desirable to accelerate the reaction.  For the introduction of one acyl group, about 1.25 mol. of acylating agent per mol. of ketimine is sufficient.  If, however, there is a hydroxyl or amino group present in the molecule which may react with the acylating agent, the proportion of the latter should be increased to about 2.5 mols.  The reaction may take place at normal, sub- or superatmospheric pressure, at a temperature depending on the nature of the reactants and any solvent that may be used.  The acylated ketimine may be separated by fractional distillation.  The hydrolysis of the ketimine may be effected with water, basic solutions or preferably acidic solutions, a number of suitable inorganic and organic acids being specified. The temperature may range from about 20 DEG  C. up to the boiling point of the reactant or any solvent that may be used.  If the reactants do not form a single phase mixture and no solvent is employed, effective contact is ensured by stirring, shaking or passing in a stream of an inert gas.  The diketone may be isolated from the reaction mixture by distillation, preferably with steam. Examples show the preparation of (1) N-(1 : 3-dimethylbutyl)-methyl isobutyl ketimine, N-(1 : 3-dimethylbutyl)-acetylmethyl isobutyl ketimine and isovalenyl acetone, which gives a copper salt; (2) N-phenyl methyl isobutyl ketimine and the other products as in (1); (3) N-(1 : 3-dimethylbutyl) di-isobutyl ketimine giving finally 3-isopropyl-6-methyl-2 : 4-heptandione; (4) N-(1 : 3-dimethylbutyl) acetophenonimine yielding eventually benzoylacetone; (5) the same imine benzoylated and hydrolysed to dibenzoylmethane which gives a copper salt; (6) N - (1 : 3 - dimethylbutyl) - acetonimine, acetylated and hydrolysed to produce acetyl-acetone; (7) N-cyclohexyl cyclohexanonimine acetylated and hydrolysed to give 2-acetylcyclohexanone.  According to the Specification as open to inspection under Sect. 91, instead of using ketimines, the monoketones may be converted into other nitrogen-containing derivatives such as oximes, phenylhydrazones or semicarbazones.  It is also stated that the radical substituted on the nitrogen atom of the imino group may be alkenyl or cycloalkenyl (suitable such groups being specified) or may be a hydrocarbon radical substituted by non-interfering groups such as halogen, ether, tertiary amino, keto, ester or carboxyl. The radicals attached to the carbon atom which is doubly-linked to the nitrogen atom may also be alkenyl or cycloalkenyl (suitable such groups being specified) or may be a hydrocarbon radical substituted by non-interfering groups such as halogen, ether or keto.  It is also stated that phthalic anhydride and maleic anhydride may be used as acylating agents.  This subject-matter does not appear in the Specification as accepted.